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Hormones and homeostasis
?Hormones
?Homeostasis
Name some endocrine glands
Hormones versus neurotransmitters…
Hormones can be steroids, proteins or
tyrosine derivatives (amines)
Steroid hormones
•
•
•
•
Derivatives of cholesterol
Insoluble in water – travel in plasma bound to plasma proteins
Longer-acting and act INSIDE the cell
Stress, sexuality, SEX
Steroid hormones
• Steroid hormones pass through the cell
membrane easily and act on the inside of
the cell
• Intracellular effects
• Bind to receptors in cytoplasm OR nucleus
• Steroid hormones alter DNA transcription:
they act as ‘transcription factors’…
Steroid hormones are transcription factors
Amine hormones
• Derived from the amino
acids tyrosine,
tryptophan, glutamine
• Produced by - the
adrenal gland, brain,
hypothalamus and the
anterior pituitary gland
• Catecholamines have very
short duration of action –
act as neurotransmitters
as well as hormones
Melatonin (tryptophan derivative)
Serotonin (Glutamine derivative)
Peptide/ protein hormones (there are
many!)
Peptide and protein hormones
• Soluble in plasma but cannot cross the
lipid membrane
• Act on cell surface receptors
• Binding with the receptor leads to
activation of a ‘second messenger’
cascade
• May or may not affect transcription in
the nucleus
Protein hormones act via ‘second
messengers’
In summary….
Hormonal control
The hypothalamus and the pituitary gland
are closely related
The hypothalamus links the nervous
and the endocrine system
• Hypothalamus controls synthesis and release of
MANY hormones from the anterior pituitary (via
releasing factors and portal circulation)
• Hypothalamic neurosecretory cells release
hormones (oxytocin, ADH) from the posterior
pituitary gland
• Negative feedback plays a major role
Hypophyseal portal circulation
Hormones secreted by the
hypothalamus/pituitary…
How does the hypothalamus orchestrate
the autonomic nervous/endocrine system?
Negative feedback is essential to
hypothalamo-pituitary-hormonal control
• Hormones whose
secretion is regulated by
the hypothalamus and
pituitary gland regulate
their own release through
negative feedback.
• The hormone produced
by a peripheral glad will
bind to receptors in the
hypothalamus and
pituitary and inhibit
release of ‘tropic’
hormones’
Explain the control of ADH secretion
by negative feedback
Thyroid hormone release is controlled
by negative feedback…